A sodium secondary battery is a nonaqueous electrolyte secondary battery. Since sodium constituting a sodium secondary battery is a material which is abundant in resource quantity and low in price, the mass supply of large-size power sources is expected by means of putting sodium secondary battery to practical use.
A sodium secondary battery usually includes an electrolyte and at least one pair of electrodes of a positive electrode including a positive electrode active material capable of doping and dedoping sodium ions, and a negative electrode including a negative electrode active material capable of doping and undoping sodium ions.
The electrode includes a current collector, and an electrode mixture formed on the said current collector. The electrode mixture includes an electrode active material such as a positive electrode active material or a negative electrode active material, a conductive material and a binder. The conductive material has a function of giving conductivity to the electrode mixture, and is necessary to bring out the performance of the electrode active material sufficiently. Examples of the conductive material include carbon materials such as acetylene black, and it has been known to use such a conductive material for a sodium secondary battery electrode (Patent Document 1).